Constitutive expression of a grape aspartic protease gene in transgenic Arabidopsis confers osmotic stress tolerance

Aspartic proteases are involved in various processes of plant senescence, programmed cell death, reproduction and stress responses. We previously identified a salt and drought stress induced gene, VlAP17, encoding a Group C aspartic protease. Here, we report its functional analysis through the characterization of transgenic Arabidopsis thaliana plants overexpressing VlAP17 under the control of constitutive promoter. The transgenic plants showed enhance salt and drought stress tolerance during seed germination as well as the seedling and mature plant stage. In additional, various stress responses indicators were analyzed and results suggested that osmotic stress caused less damage to the plasma membrane of transgenic seedlings than to that of wild type plants. VlAP17 overexpression also resulted in increased ABA levels, a reduction in average stomatal aperture size, and elevated expression levels of stress-response genes involved in the ABA-dependent pathway, as well as higher activities of several antioxidases: superoxide dismutase, catalase and peroxidase. Taken together, these findings suggest that VlAP17 plays a role in protecting the integrity of plasma membrane and it may also be involved in, or have a function upstream of, the ABA biosynthetic pathway.